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Price (Pick-up CBD, around the university): $5 if you bring your own container/bag, $7 if not, in exact change. Price (postage-included price, overnight courier only): $18.50 for one small bottle, $20 for two small bottles. They'll actually survive a week in regular non-courier post most of the time but overnight courier is worth the peace of mind and doesn't make much difference in the long run. I would prefer pick-up as postage takes about half an hour of my finite lifetime that I'd rather spend drinking tea and fencing and being a responsible, productive citizen, or earning minimum wage. Quantity: A minimum of two dozen mature females if picking up, a maximum of a dozen per bottle if posting. They will run out of oxygen if posted in a sealed container at high density. At a dozen per bottle and overnight courier I have always had survivors, and would be willing to refund if you can show me a photo with twelve dead daphnia on arrival. All you need is one live female to guarantee yourself a colony, as population usually triples every week under good growth conditions. Start with a dozen, and after 8 weeks you'll have more than 70,000 if you aren't limited for space, light, or nutrients. What they are and what they are good for: Daphnia carinata are a common freshwater zooplankton in New Zealand that you can easily culture for most small-to-medium-sized fish. They eat suspended microorganisms such as algae, and because of that are quite nutritionally-balanced (algae produce stuff like Omega-3's that fish can't synthesise on their own). They usually reproduce asexually (are all female) and usually give birth to live young, but under adverse conditions will tend to produce males who then reproduce with the females to produce dormant resting eggs. Mine haven't done so in years. The mature females are about 4.5 mm, which is still large enough for the average goldfish and small enough for mature Betta splendens and neon tetras, but may be too big for smaller minnows to fit in their mouths. Newborns may be too large for most newborn fish fry except guppies to eat. If you have microworms though, you can feed fry from newly-hatched up to a size that can eat D. carinata. A combination of sieve and fine-meshed net usually can separate out different sizes of Daphnia. You can find them in many rural stock troughs and lakes. If it's about 4 mm long and looks like a typical daphnia, it is probably D. carinata. If the adults are smaller (0.5 mm? about the size of newly hatched brine shrimp), it's probably Ceriodaphnia. I have some Ceriodaphnia but none to spare yet - Ceriodaphnia are a very adequate BBS substitute due to their size (although microworms are a more convenient BBS substitute). How to grow them: They do fine outdoors anywhere in New Zealand, in full sun or semi-shade in a reasonable-sized open container such as a 10 L bucket. Indoors is a different story. I do not recommend indoor culture unless you have daphnia to spare to try it out. Preparation: leave water from aquarium water-change (assuming normal pH) or rain water out in the sun for a while (maybe a week), with a small layer of clean dirt (about 2 mm, say) for nutrients and stability. They can also be cultured with blackworms if you use this layer of dirt. Obviously, use dirt which sinks, not potting mix. Maintenance: do small (5-10%), regular water-changes when you harvest, to be safe. It's fairly easy to just scoop up culture water and pour through a net, and then replace that same amount of water plus a bit more to account for evaporation. I get away with no water changes in my back-up cultures, somehow, but I do not recommend this. I've kept a back-up culture going for years on my balcony in a sealed peanut-butter jar but that jar is a lucky jar. I do not recommend this for a regular culture container - just get a bucket or old fish tank as if the container is too small it will be more at risk of crashing. Back-up cultures are very important.